#include <iostream>
#include <fstream>
using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int NumarZerouri(int n);
int CautareBinara();

const int INF = 500000000;
int P;

int main()
{
    fin >> P;

    fout << CautareBinara();

    return 0;
}

int CautareBinara()
{
    int st(1), dr(INF), mij, rez(-1);

    while (st <= dr)
    {
        mij = st + (dr - st) / 2;

        int zero = NumarZerouri(mij);

        if (zero >= P)
        {
            rez = mij;
            dr = mij - 1;
        }
        else
            st = mij + 1;
    }

    return rez;
}

int NumarZerouri(int n)
{
    int total(0);

    while (n >= 5)
    {
        total += (n / 5);

        n /= 5;
    }

    return total;
}